This application claims the priority of Korean Patent Application No. 10-2005-0036536, filed on Apr. 30, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a compact zoom lens, and more particularly, to a zoom lens which decreases the number of lenses needed by an imaging optical system using a solid-state image sensing device, thereby providing compact size and reducing overall length for the optical system while providing excellent telecentricity, high magnification, and high imaging performance.
2. Description of the Related Art
Generally, a zoom lens used in a still camera and a video camera requires excellent optical performance, high magnification, and compactness. Moreover, with the widespread use of electronic equipment such as a portable information terminal (e.g., a personal digital assistant (PDA)) and a mobile terminal, a digital camera or a digital video unit is increasingly installed in such electronic equipment. As a result, there is an increased demand for compactness of the camera module. In an optical system having a solid-state image sensing device, such as a charge coupled device (CCD) or a complimentary metal-oxide semiconductor (CMOS), which is used for electronic still cameras and video cameras, since a crystal filter is used to prevent a moire phenomenon caused by the periodic structure of the image sensing device, a sufficient back focal length and telecentricity of light incident onto an image surface are needed taking account of the thickness and position of the crystal filter. In addition, the sum of thicknesses of lenses and an overall optical length must be short to reduce the length for receiving the optical system.
An example of a conventional zoom lens using three-group zoom technology is the zoom lens disclosed in Japanese Patent Publication No. 2000-111798. This zoom lens has high imaging performance at high magnification. However, since a first lens group includes three lenses and the overall length of an optical system is long, it is difficult to make the zoom lens compact and thin.
Referring to FIG. 1, which illustrates a zoom lens disclosed in Japanese Patent Publication No. 2002-277740, the zoom lens sequentially includes a first lens group 10 having a negative refractive power, a second lens group 20 having a positive refractive power, and a third lens group 30 having a positive refractive power. The first lens group 10, the second lens group 20, and the third lens group 30 are moved to zoom in or out and a high zoom ratio is accomplished. However, a disadvantage of this zoom lens is that it requires an increase in the number of lenses and an increase in the thickness of each lens group. Even if the total number of lenses is decreased to 6, since the thickness of the second lens group 20 and the third lens group 30 is increased, it is difficult to make the zoom lens compact and thin.
A zoom lens disclosed in Japanese Patent Publication No.2001-272602 includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power and changes power by changing the distance between the lens groups. The first lens group includes a single negative lens and a single positive lens. The second lens group includes a pair of doublets and a single positive lens. The third lens group includes at least one positive lens. Although this zoom lens achieves compactness, it does not achieve high magnification.
To achieve compactness of the camera module and the lens system, miniaturization is important. Furthermore, recently, providing a lens system that is thin is increasingly important.